The present invention relates to an electromagnetic valve for use in a semiconductor manufacturing apparatus, which opens and closes a process-gas flow passage.
Conventionally, a pneumatic valve of the type shown in FIG. 1 has been used for opening and closing a process-gas flow passage in a semiconductor manufacturing apparatus (reference is made to, for example, U.S. Pat. No. 5,253,671 and Unexamined Japanese Patent Application Public Disclosure No. 2002-250451). In order to open and close the valve of this type, N2 (a nitrogen gas) is externally supplied to or discharged from an actuator portion of the valve through a tube, and a stroke of a piston as an actuator is effected by utilizing a pressure of the gas. In this arrangement, a structure for actuating the valve is relatively simple, thus reducing the possibility of malfunctioning and resulting in wide use of the valve of this type. However, due to the time required for supplying or discharging N2 to or from the actuator portion, retardation of valve opening or valve closing occurs, thus limiting the speed of the valve in a high-speed operation. Further, when a plurality of valves are used, it is difficult to open and close the valves simultaneously due to, for example, the N2-supply tubes having different lengths being used for the respective valves. Thus, the valve of this type is unsuitable for a high-speed operation.
A solenoid valve utilizing a solenoid as an actuator has also been used (reference is made to, for example, U.S. Pat. No. 5,862,995). A solenoid valve has a high speed of operation as compared to a pneumatic valve. However, in a solenoid valve, a valve body is formed from a cushioning material such as rubber, so as to prevent leakage of the gas when the valve is closed, and this cushioning material causes generation of impurities. Therefore, there is a tendency of avoiding use of a solenoid valve for a semiconductor manufacturing apparatus.
It has also been proposed to employ a valve in which a valve body is made of a metal, not a cushioning material such as rubber (reference is made to, for example, U.S. Pat. No. 5,755,428). In this valve, at a time the valve is closed, a valve head collides against a valve seat with a large force, thus decreasing the life of the valve.
In order to suppress an impact of a valve body during a valve operation, it has been proposed to use a valve in which a squeezed film is utilized (reference is made to, for example, Unexamined Japanese Patent Application Public Disclosure No. 9-72435). However, the valve of this type is unsuitable for a high-speed operation, especially under reduced pressure.